remedial measures are to be used, this extra corrosion just below the 



mud line may be provided for by applying pads of extra metal before driving 

 the pi].es if the ultimate location of the mud line can be determined 

 accurately enough in advance. Othorvn.se, it may be possible to install 

 reinforcing shields or collars after the piles have been driven. The 

 actual ne d for these steps vjill be difficult to determine in advance 

 unless there is some direct experience with other steel piles in the same 

 localitj'- to serve as a guide, 



Ihe most effective way to prevent corrosion underground will be the 

 a plication of cathodic protection, preferably as a supplement to an 

 orgaaic coating which will be helpful in reducing the current requirements 

 and achieving distribution of the protective current throughout the buried 

 length of the pile. Coal tar enamels and vinyl coati.nj's represent good 

 choices of coating for this purpose. Since cathodic protection of the 

 underground surfaces will alivays be associated with cathodic protection 

 of the undeiTirater surfaces, the current requirements will be established 

 for the combi.ned areas and it seems safe to assume that the criteria of 

 protection used for the underwater areas will automatically include the 

 u.nderground surfaces as well. 



Zone 2 - At the imd Line 



In addition to the accelerated attack in the region just below the mud 

 line already discussed, there may be very nevere erosion at the mud line 

 itself. Tliis will occur on piles driven in shallow water on a beach where 

 the action of the vjaves will cause severe scouring by sand held in sus- 

 pension. This may proceed at rates of thinning as high as 0.05 inch per 

 year frora each sux'face exnosed to the scouring action. Such rates have 

 been observed on sheet steel piling in the jetties at Kure Beach and in 

 certain groins at Palm Beach as described by C. '. Ross-'- of the Beach 

 Erosion Board, 



Although this attack probably involves considerable corrosion of surfaces 

 freshly exposed by abrasion, there is so much simple mechanical vrearing 

 away that it seems unl.ikely thrt cathodic protection would prevent this 

 scouring action. Nor are ordinary protective coatings likely to survive 

 long enough to be effective, V/ooden and concrete shields have been used 

 with spotty success, vfood, of course, would have to be treated vifith pre- 

 servatives against marine borers. Concrete is su-bject to cracking and 

 spalling - especially if corrosion of the underlying steel is not arrested 

 completely, 



E;cperience with piles in such a location as described by Kartinen^ of the 

 Signal Oil & Gas Com-^anj^ demonstrated an ama/jing effect of the shape of 

 the pile in reducing mud line erosion. The vesting of a tubular section 

 was found to be only a small fraction of that of conventional 'H ' pile 



. .-...■- 



■^C. W. Ross, "Deterioration of Steel Sheet Pile Groins at Palm Beach, 

 Florida," CORROSION, Vol. 5, 19)-i9, p. 339. 



E, Kartinen, ''Discussion at Sea Horse Institute Informal Conferences, 19^1-52, 



E _ 2 



